"Umpolung" photoinduced charge separation in an anion-bound supramolecular complex.
A new supramolecular system, consisting of an expanded porphyrin, cyclo[8]pyrrole (C8) and a pyrene carboxylate (Py) is capable not only of electron transfer upon photoexcitation, but results in "umpolung" or a reversal of the predicted charge-separation behavior in that the higher energy radical ion pair, C8.+-Py.- (2.58 eV) is formed as opposed to C8.--Py.+ (1.31 eV). This observation is rationalized in terms of the latter radical ion pair, C8.--Py.+ being in the Marcus inverted region. Transient absorption spectral studies reveal a charge-separated lifetime of 300 micros, which decays to the triplet state of cyclo[8]pyrrole, also an exceedingly long-lived species. The novel features of this noncovalent dyad highlight the potential utility of anion binding in the construction of supramolecular electron transfer systems.
Sessler
Jonathan L
JL
Department of Chemistry & Biochemistry, University Station-A5300, The University of Texas, Austin, Texas 78712-0165, USA. sessler@mail.utexas.edu
Karnas
Elizabeth
E
Kim
Sung Kuk
SK
Ou
Zhongping
Z
Zhang
Min
M
Kadish
Karl M
KM
Ohkubo
Kei
K
Fukuzumi
Shunichi
S
D000838:Anions / Q000737:chemistry; D008956:Models, Chemical; D015394:Molecular Structure; D009930:Organic Chemicals / Q000737:chemistry*; D010777:Photochemistry; D013053:Spectrophotometry
D000838:Anions; D009930:Organic Chemicals